/Engine/Source/Runtime/Slate/Public/Widgets/Layout/SWindowTitleBarArea.h
Called when the maximize/restore button or double click needs to toggle fullscreen. We don't have access to GEngine inSWindowTitleBarArea, so the GameLayerManager or UMG widget will handle this.
WidgetArgsType & RequestToggleFullscreen &40; const FSimpleDelegate & InDelegate &41;